Unnecessary Echoes - Furuno FSV-25 Operator's Manual

2. HORIZONTAL MODE
2.23.2

Unnecessary echoes

Sea surface reflections
To reduce sea surface reflections, set the tilt angle to 4° or higher, so the upper edge
of the sonar beam does not hit the sea surface, or adjust near gain. When a decreased
tilt is used, sea surface reflections cover a large area as illustrated below.
Tilt: 0°
Tilt: 4 - 5°
Wake
A wake produced by own ship or another ship can be a strong reflecting object when
a decreased tilt angle is used. As the wake appears as a thick continuous line, it can
be easily distinguished from a school of fish. A wake contains many air bubbles which
attenuate ultrasonic energy, making it difficult to sound beyond the wake.
Other ship
Own
ship
2-42
Sea surface
10°
Sea surface
11°
Own ship's
screw noise
Wake produced
by other ship
Tilt angle
indication
Sea surface
reflections
Own ship's wake
Own ship's
(produced when
screw noise
own ship turned)